A toothed belt is known comprising a body made of elastomeric material, embedded in which is a plurality of longitudinal filiform resistant inserts, also referred to as “cords”, and a plurality of teeth coated with a coating fabric.
Each component of the belt contributes to increasing the performance in terms of mechanical resistance so as to decrease the risk of failure of the belt and increase the specific transmissible power.
The coating fabric of the belts increases the resistance to abrasion and hence protects the working surface of the belt from wear due to rubbing between the sides and the slanting surfaces of the teeth of the belt and the sides and the bottom lands of the races of the pulley with which the belt interacts.
Furthermore, the coating fabric reduces the coefficient of friction on the working surface and reduces the deformability of the teeth, thus preventing failure.
The coating fabric used may be constituted by a single layer or, alternatively, may be double-layered so as to guarantee greater sturdiness and stiffness.
The fabric is normally treated with an adhesive, for example resorcinol and formaldehyde lattice (RFL) to increase adherence between the body and the fabric itself.
There are moreover employed a number of methods for increasing resistance to wear of drive belts by modifying the structure of the coating fabric or performing different treatments on the fabric, for example, treatments of the fabric with halogenated polymers.
Said treatments do not, however, lead to any great increase in resistance to wear in so far as the coating fabric of the toothed belt, in use, constitutes in any case the working surface.
To overcome the above problem, the patent EP1157813 filed in the name of the present applicant proposed coating the coating fabric with a resistant layer comprising a fluorinated plastomer, an elastomeric material, and a vulcanizing agent. The fluorinated plastomer is present in the resistant layer in an amount greater than that of the elastomeric material.
The use of said resistant layer has enabled excellent results in terms of increase in resistance to wear to be obtained.
The resistant layer is formed via the use of a fluorinated plastomer comprising particles which have an average size of 20 μm or more and are in the form of agglomerates. Consequently, said agglomerates have sizes such as to entail a difficult mixability in solution with the elastomer. The agglomerates are hence also present in the final resistant layer that is consequently non-homogeneous, and said lack of homogeneity can generate a high level of noise.
Research has hence been carried out into solutions that will enable, together with a high resistance to wear, also an improved and lower level of noise during operation of the toothed belt to be achieved.